This invention relates to an analytical reagent suitable for the colorimetric determination of cyanide ions in liquids, and to the production of new colored compounds.
The determination of cyanide has been based on a reaction, known for a long time, wherein cyanide and the active chlorine from chloramine-T (sodium para-toluenesulfonic acid chloramide) are reacted to cyanogen chloride which splits a pyridine ring with the formation of glutaconic dialdehyde. This dialdehyde condenses with two molecules of a suitable organic compound to a colored polymethine compound. Organic compounds which have been recommended for this purpose are barbituric acid [Z. analyt. Chem. [Journal of Analytic Chemistry] 138, 414 [1953]), pyrazolones (Anal. Chem. 19, 272 [1947])], and benzidine ("Deutsche Einheitsverfahren zur Wasseruntersuchung" [German Standard Methods for Water Testing] D 13, 1971, p. 5). These organic compounds have, however, a number of disadvantages which render them essentially useless as a ready-to-use analytical reagent for the detection of cyanide for general purposes, for example, outside of the laboratory.
Specifically, solutions of these organic compounds have a short shelf life: after about two months, barbituric acid in water and pyridine fail to yield exact analytical results, and after about three months, at room temperature, barbituric acid in dimethyl sulfoxide results in sedimentation. (These sediments form in only a few days if the reagent is stored at 42.degree. C.) As for the pyrazolone reagent, it must be prepared fresh daily, since a pink color appears only after two days, and the color of the thus-produced polymethine dye is unstable. Lastly, the benzidine reagent is not only too insensitive, but also carcinogenic.